The Subhercynian Basin: an example of an intraplate foreland basin due to a broken plate

David Hindle,Jonas Kley

doi:10.5194/se-12-2425-2021

Abstract

Abstract. The Late Cretaceous intraplate shortening event in central western Europe is associated with a number of marine basins of relatively high amplitude and short wavelength (2–3 km depth and 20–100 km width). In particular, the Harz Mountains, a basement uplift on a single, relatively steeply dipping basement thrust, have filled the adjacent Subhercynian Cretaceous Basin with their erosive product, proving that the two were related and synchronous. The problem of generating subsidence of this general style and geometry in an intraplate setting is dealt with here by using an elastic flexural model conditioned to take account of basement thrusts as weak zones in the lithosphere. Using a relatively simple configuration of this kind, we reproduce many of the basic features of the Subhercynian Cretaceous Basin and related basement thrusts. As a result, we suggest that overall, it shares many characteristics with larger-scale foreland basins associated with collisional orogens on plate boundaries.

Highlights

The Subhercynian Cretaceous Basin (SCB) is a narrow (∼ 20 km) but relatively thick (∼ 2500 m at its depocentre), mostly shallow marine trough with a WNW–ESE-oriented subsidence axis extending ∼ 90 km along the northern edge of the Harz Mountains in central Germany
The Harz Northern Boundary Fault (HNBF) is a WNW– ESE-trending basement thrust that offsets a “Variscan” basement (Devonian to Carboniferous metasedimentary rocks with some granitic intrusions deformed by the Variscan orogeny) and its Late Paleozic and Mesozoic cover along a ∼ 100 km long zone
The SCB is underlain by a Mesozoic cover of Triassic, Jurassic, and some Lower Cretaceous material, which in turn overlies upper Permian Zechstein evaporites that act as a décollement horizon accommodating some Late Cretaceous shortening (Fig. 3)

Summary

Introduction

The Subhercynian Cretaceous Basin (SCB) is a narrow (∼ 20 km) but relatively thick (∼ 2500 m at its depocentre), mostly shallow marine trough with a WNW–ESE-oriented subsidence axis extending ∼ 90 km along the northern edge of the Harz Mountains in central Germany (von Eynatten et al, 2008; Voigt et al, 2008). The SCB has a depocentre directly adjacent to the Harz Northern Boundary Fault (HNBF), and despite being syn-tectonically folded, the Late Cretaceous infill is clearly asymmetrically distributed, with its maximum sedimentary thickness along the HNBF, wedging out to the north over a minimum of 25 km distance (Fig. 2). In this way, the basin geometry resembles a foreland basin, which is a unique example of marine basins in compressional settings on Earth. A number of different mechanisms (Voigt et al, 2008; von Eynatten et al, 2008) have been associated with SCB formation and to a lesser degree subsidence, an explicit analysis of the mechanics of elastic flexural bending has not been presented

Foreland Basin character of the SCB

Broken lithosphere and the structural evolution of the HNBF and SCB

Flexure models of the broken central European lithosphere

Implications of the model

Conclusions